[Rikosintie]

I think you should replace them. Here is a link for new ones. They are at the bottom of the page.
BellissiMoto - AEM Factory Ducati Sprockets and Carrier

Since you already have it apart that "light weight hub" looks nice too!
Michael

 

[Thermal Runaway]

Cracked doesn't seem normal to me, I would replace them. Honestly surprised they lasted as long as they did since they are just cheap rubber.